Ab Initio Insight into CsHMoO<sub>4</sub> and H<sub>2</sub>MoO<sub>4</sub> Complexes on MoO<sub>3</sub> Surfaces

Solid\nsurfaces play a crucial role in many processes, yet their\nimpact on nuclear safety is not well understood. This study investigates\nhow solid surfaces affect the behavior of radioactive gaseous species,\nfocusing on the interaction of fission product complexes formed under\nnuclear accident conditions. Specifically, we examine the condensation\nand decomposition of Cs–Mo complexes, CsHMoO<sub>4</sub> and\nH<sub>2</sub>MoO<sub>4</sub>, when interacting with MoO<sub>3</sub> deposits in a reactor cooling system, considering two surface terminations:\nO and Mo. Using density functional theory (DFT), we calculate the\nGibbs free energy for these reactions on MoO<sub>3</sub> surfaces\nat temperatures ranging from 300 to 1800 K. CsHMoO<sub>4</sub> condenses\nbelow 850 K and dissociates between 300 and 650 K on O-MoO<sub>3</sub> and 650–1250 K on Mo-MoO<sub>3</sub>, forming Cs<sub>2</sub>MoO<sub>4</sub> and MoO<sub>3</sub>, along with steam release. H<sub>2</sub>MoO<sub>4</sub> condenses below 500 K and decomposes between\n600 and 800 K, but only on Mo-terminated surfaces. These findings\nimprove the accuracy of nuclear simulations, helping to predict species\ncomposition and transport within the reactor cooling system during\naccidents.